After a week living in tents in Colorado’s Rockies, volunteers’ internal clocks shifted about two hours earlier, transforming night owls into early birds, researchers report August 1 in Current Biology.

“It’s a clever study, and it makes a dramatic point,” says Katherine Sharkey, a sleep researcher and physician at Brown University. People get much more light outside than they do indoors, and that can reset their internal clocks, she says.

A master clock in the brain controls the release of melatonin, a hormone that prepares the body for sleep. Melatonin levels rise in the early evening and then taper off in the morning before a person wakes up.

But because so many people spend their days indoors and their nights bathed in the glow of electric lights, the body’s clock can get out of sync. Melatonin levels ramp up later in the evening and ebb later in the

This article is only available to Science News subscribers. Already a subscriber? Log in now. Or subscribe today for full access.